The invention relates to an apparatus for the hardening of cylindrical bearing faces of a shaft, wherein at least one of the transitional radii to the adjoining shaft portions is constructed recessed. Such apparatuses are used, for example, to harden crankshaft crankpins which are bounded laterally by cheeks. In this respect special steps are required to ensure that even the recessed transitional radii are heated to an extent adequate for proper hardening.
To this end in a prior art inductively operating apparatus of the kind specified, known from German Auslegeschrift DE-AS 14 83 016, the heating conductors of an inductor take the form of a parallelogram whose two parallel sides are at a different distance from one another. As a result, the inductor can first be moved with its narrow side into the space left between the shaft portions, until it is located on the bearing face to be hardened. By the rotation of the inductor, the heating conductors are then brought via their wide side to bear against the transitional radii. The inductor is forced resiliently against insulated members of the installation.
The advantage of the apparatus known from DE-AS 14 83 016 is that the inductors can be automatically applied to the bearing face to be hardened and moved into their operating position. At the same time the heating loops are so shaped that coolant can flow in circuit through them without problems. In this way the overheating of the loop material can be reliably prevented. However, one disadvantage of this prior art is the need for expensive apparatus to introduce and rotate the inductor. It has moreover been found in practice that with this prior art apparatus it is difficult to maintain a constant distance between workpiece and inductor, resulting in a deterioration in the processing result. A further important disadvantage of the prior art apparatus is that each inductor engages around the bearing face to be hardened by less than 90xc2x0. This causes the problem that heating energy can be introduced into the bearing face only to a limited extent. It has been found that frequently this quantity of energy is inadequate to ensure a proper hardening result.
To obviate the afore-explained problems, German Patent Specification DE 3 36 23 119 C1 suggested the use of an inductor divided into two halves for the inductive heating of the bearing face to be hardened. One of the inductor halves is rigidly connected to an adjusting unit, while the second inductor half is attached pivotably to the fixed unit. The adjusting unit comprises a device for applying the inductors to the bearing face to be hardened, a second adjusting device for moving the inductor axis-parallel with the longitudinal axis of the shaft, and a third adjusting device for pivoting the pivotable inductor half into its operating position. By means of the adjusting unit, the halves of the inductor can then be applied in a position bearing close against one another to the bearing face to be hardened, until the inductors are disposed thereon. Then first the fixed inductor half is moved into its working position, by being moved jointly with the pivotable inductor half axis-parallel with the longitudinal axis of the shaft. Then the pivotable inductor half is pivoted in the direction of its associated transitional radius.
Although with the apparatus known from DE 36 23 119 C1 it is simpler than in the earlier prior art to apply the inductor to the bearing face to be hardened and to move its inductor halves into the operating position, but the apparatus required for this purpose is still very expensive. It is also difficult to move the pivotable inductor half into an optimum operating position. This, and also the circumstance that in the prior art apparatus the heating conductors sweep over the bearing place to be hardened only with a gap in the central zone results in an inferior operating result. Lastly, both the electric connection and also the coolant supply of the pivotable inductor half are unreliable.
The problem of the invention, starting from the afore-explained prior art, is to provide an apparatus of the kind specified with which an improved operating result is achieved using less expensive apparatus.
This problem is solved according to the invention by an apparatus for the hardening of cylindrical bearing faces of a shaft, wherein at least one of the transitional radii to the adjoining shaft portions is constructed recessed, having: a pair of inductively operating heating units, which are each formed at least by one inductor having two spaced-out heating conductor branches each extending in the peripheral direction of the bearing face and which are connected to a power supply, one outer heating conductor branch of the inductor of one heating unit being associated with the first transitional radius, and an outer heating conductor branch of the inductor of the other heating unit being associated with the second transitional radius, while in each case the inner heating conductor branches of the inductors are disposed adjacent one another; an adjusting device for the purpose of adjusting the inductors simultaneously from the radial direction on to the bearing face to be hardened, until the inductors are applied to the bearing face, the heating conductor branches engaging at least partially around the bearing face in this state, and the inner heating conductor branches of the two inductors, viewed in the peripheral direction, registering contactlessly with one another in an overlap zone, and a second adjusting device for the purpose of moving at least the inductor associated with the recessed radius after application to the bearing face by a movement directed axis-parallel with the longitudinal axis of the shaft in the direction of the recessed transitional radius, until its outer heating conductor branch has moved into the particular transitional radius. Preferably each heating unit has at least one power supply.
The apparatus according to the invention is equipped with two independent heating units, each of which comprises an inductor and at least the associated power supply device. This obviates the need for unreliable connections of the electric supply of the inductors, the heating unit associated with each of them and the coolant supply. Any quenching sprays possibly additionally borne by the heating units can be supplied with quenching fluid without problems.
In the apparatus according to the invention the dimensions and external shape of the inductors of the two heating units are so adapted to one another that, in dependence on the application, either one inductor or both inductors jointly and simultaneously can be applied in a closely adjacent position to the shaft. In this position, the total width of the two inductors, measured in the axial direction of the shaft, is smaller than the width of the free space left between the shaft portions adjoining the bearing face to be hardened, so that there is no risk of any collision during the introduction of the inductors into the free space.
Due to the independence of the heating units, conventional simple adjusting devices can bring the inductors on to the bearing face with great accuracy. Similarly conventional precisely operating adjusting devices can be used to move the inductors into their final working position, in a movement directed axis-parallel with the longitudinal axis of the shaft. In this position the outer heating conductor branches of the inductors are disposed in the transitional radii associated therewith.
Due to the independence of the heating units moreover the simplest steps, for example the use of sliding pieces, can ensure without problems that the inductors maintain their working position during processing. Even in this way the result of processing in the zone of the transitional radii is improved as against conventional apparatuses of the kind by an apparatus constructed according to the invention.
The fact that the inner heating conductor branches of both inductors disposed one beside the other are also designed in such a way that they overlap one another contact-free, viewed in the peripheral direction, ensures that at the same time as the zone of the transitional radii, the entire surface of the bearing face to be hardened is heated to an extent adequate for the particularly hardening required.
Preferably measured in the axial direction of the shaft the width of the overlap zone is greater than the sum of the depths of the transitional radii. This ensures that the inner heating conductor branches of the two inductors also overlap one another in the operating position. One feature of the invention making this possible is characterised in that the heating conductor branches disposed adjacent one another are disposed at an angle, referred to the heating conductor branches associated with the transitional radii.
A particularly preferred embodiment of the invention is characterised in that the inductors engage around the bearing face to be hardened by more than 90xc2x0, preferably by more than 140xc2x0.
In dependence on the amount of heat to be introduced into the bearing face, conveniently the adjacent inner heating conductor branches are shorter than the outer heating conductor branches each associated with the transitional radii.
A preferred feature of the invention of practical relevance is characterised in that the heating conductor branches are each divided into two component parts. In this way, for example, sliding pieces can be positioned problem-free at those places at which they are required for the optimum guiding of the inductors during processing.
Another advantageous feature of the invention is characterised in that the purpose of the adjusting device operative in the radial direction is to move the heating units including the conductors as one whole. It can also be advantageous if the purpose of the adjusting device operative in the axial direction is to move the heating units including the inductors, as one whole. In this way an enhancement of operating safety can be accompanied by a further reduction of expenditure for the connections between the inductors and the power and coolant supply devices respectively.
The apparatus according to the invention is particularly suitable for the hardening of crankshaft crankpins laterally bounded by cheeks, wherein the transitional radii are recessed into the cheeks and wherein, due to the generally large height of the cheeks, the free space available for the introduction of the inductors is particularly limited.